From owner-freebsd-current  Tue Dec  1 22:35:30 1998
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Date: Wed, 2 Dec 1998 17:35:01 +1100
From: Bruce Evans <bde@zeta.org.au>
Message-Id: <199812020635.RAA13376@godzilla.zeta.org.au>
To: bde@zeta.org.au, mike@smith.net.au
Subject: Re: sio breakage
Cc: andyf@speednet.com.au, freebsd-current@FreeBSD.ORG, geoffb@demon.net,
        johan@granlund.nu, ortmann@sparc.isl.net
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>> something()
>> {
>> 	asm("cli");
>> 	asm("sti");
>> }
>> 
>> This disables interrupts for 0 user instructions, but if a pagefault
>> occurs for reading the "sti" instruction, it disables interrupts for
>> hundreds, thousands or millions of kernel instructions.
>
>Since 'cli' can't be executed in user space, and a page fault in kernel 
>mode is a fatal occurrence, this can't happen.

man 4 io.

Bruce

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